I think $7-8/hr is reasonable if we are talking about a 13 year old and all they have to do is play with your (1 or 2) kids for 1-2 hours, put them to bed and then watch a movie. Now add more kids, or difficult kids, or a baby then up it a bit. Also, as they get older and more experienced I would pay more. I would also pay more if they are 16 and older and driving to and from your place.

My current babysitter is 16, drives, and my kids are 9 and 11. We vary the rate slightly depending on circumstances, but usually between $10-12/hr. And I always make sure we round up so we don't seem cheap. Worth pointing out, when we started using this babysitter 4 years ago, her parents and her said $5/hr was enough. We never paid less than $6 at the beginning and slowly increased since then.